A. Background Regarding Squalamine
Chemically squalamine presented a structure never before seen in nature that being a bile acid coupled to a polyamine (spermidine):

The discovery of squalamine, the structure of which is shown above, was reported by Michael Zasloff in 1993 (U.S. Pat. No. 5,192,756). Squalamine was discovered in various tissues of the dogfish shark (Squalus acanthias) in a search for antibacterial agents. The most abundant source of squalamine is in the livers of Squalus acanthias, though it is found in other sources, such as lampreys (Yun et al., “Identification of Squalamine in the Plasma Membrane of White Blood Cells in the Sea Lamprey,” Petromyzon marinus,” J. Lipid Res., 48(12): 2579-2586 (2007)).
Numerous studies later demonstrated that squalamine exhibits potent antibacterial activity in vitro (Salmi, Loncle et al. 2008). Subsequently, squalamine was discovered to exhibit antiangiogenic activity in vitro and upon administration to animals (Sills, Williams et al. 1998; Yin, Gentili et al. 2002). As a consequence, squalamine has been evaluated in disease states known to be associated with pathological neovascularization, such as cancer (Sills, Williams et al. 1998; Schiller and Bittner 1999; Bhargava, Marshall et al. 2001; Williams, Weitman et al. 2001; Hao, Hammond et al. 2003; Herbst, Hammond et al. 2003; Sokoloff, Rinker-Schaeffer et al. 2004), and vascular disorders of the eye, including macular degeneration (US2007/10504A1 2007), retinopathy of prematurity (Higgins, Sanders et al. 2000; Higgins, Yan et al. 2004; US2007/10504A1 2007), corneal neovascularization (Genaidy, Kazi et al. 2002) and diabetic retinopathy (US2007/10504A1 2007).
The utility of squalamine as an anti-infective has been demonstrated in vitro against bacteria and fungi (Moore, Wehrli et al. 1993; Rao, Shinnar et al. 2000; Salmi, Loncle et al. 2008). Squalamine is a cationic amphipathic substance exhibiting an affinity for membranes composed of anionic phospholipids (Selinsky, Zhou et al. 1998; Selinsky, Smith et al. 2000). Like other such agents, including magainin and cationic antimicrobial peptides, squalamine is believed to exert antimicrobial action by interacting electrostatically with the membranes of target microorganisms, which generally display anionic phospholipids on the membrane surface exposed to the environment, subsequently disturbing their functional integrity, and causing death of the targeted microbe (Sills, Williams et al. 1998; Zasloff 2002; Salmi, Loncle et al. 2008).
To date, squalamine has not been reported to display efficacy as an anti-infective in a living animal. In no published patent application or issued patent has such evidence been reported (U.S. Pat. Nos. 5,192,756; 5,637,691; 5,721,226; 5,733,899; 5,763,430; 5,792,635; 5,795,885; 5,840,740; 5,840,936; 5,847,172; 5,856,535; 5,874,597; 5,994,336; 6,017,906; 6,143,738; 6,147,060; 6,388,108; 6,596,712; U.S. Patent Publication No. 2005/0261508A1 2005; U.S. Pat. No. 6,962,909; U.S. Patent Publication No. 2006/0166950A1 2006; U.S. Patent Publication No. 2006/0183928A1 2006; U.S. Patent Publication No. 2007/10504A1 2007).
Recent studies have revealed that squalamine is inactivated by the concentrations of ionized calcium and magnesium present in mammalian blood, preventing squalamine from exerting its antimicrobial activity in the setting of systemic bacterial, fungal, or protozoan infections (Salmi, Loncle et al. 2008).
Most studies of mechanism of squalamine have focused on the effects of squalamine on properties of the endothelial cell. The compound has been shown to inhibit many downstream effects stimulated by diverse growth-factors (VEGF, thrombin, FGF) including cellular proliferation, cellular migration, vascular tube formation, sodium-proton anti-porter activation. (Sills et al., “Squalamine inhibits angiogenesis and solid tumor growth in vivo and perturbs embryonic vasculature,” Cancer Res 58, 2784-92 (1998); Li et al., “Squalamine and cisplatin block angiogenesis and growth of human ovarian cancer cells with or without HER-2 gene overexpression,” Oncogene 21, 2805-14 (2002); Akhter et al., “Squalamine, a novel cationic steroid, specifically inhibits the brush-border Na+/H+ exchanger isoform NHE3,” Am J Physiol 276, C136-44 (1999); and Williams et al., “Squalamine treatment of human tumors in nu/nu mice enhances platinum-based chemotherapies,” Clin Cancer Res 7, 724-33 (2001)).
No mention of squalamine's use as a systemic antimicrobial agent, for example, appears in a recent patent application (U.S. Patent Publication No. 2007/10504A1), which describes a favored salt form of squalamine for therapeutic administration, and which addresses the utility of squalamine as a systemic agent in the treatment of disorders of neovascularization and cancer.
To date, no published data describe or support the efficacy of squalamine in treating or preventing a systemic viral infection in an animal. It has been reported in a patent application that squalamine could inhibit the infectivity of HIV and HSV in tissue culture (WO96/08270). However, it was not reported at that time, nor until the invention disclosed herein, that squalamine could exhibit antiviral activity when administered systemically to an animal. In the experiments described in WO96/08270, squalamine was conceived as a component of a topical agent to be used as a “chemical condom”, acting as a microbicide, and capable of rapidly inactivating HIV or HSV on contact by disrupting the outermost membranous envelopes of the viruses. Thus, the antiviral properties of squalamine observed in vitro were believed to result from direct disruption of the viral membrane, via a mechanism analogous to that proposed for its antibacterial activity. The potential use of squalamine for the topical prevention of sexually transmitted diseases such as HIV, Herpes simplex, and Neisseria gonorrhea was presented at the 1995 ICAAC conference (MacDonald 1995). Thus, squalamine was proposed to have utility as an advanced form of “disinfectant,” to be applied to a mucosal surface in some formulation and thereby prevent viable virus from gaining access to the epithelial surfaces of the genitourinary tract.
Squalamine has been shown to inhibit a specific isoform of the sodium-hydrogen exchanger (“NHE-3”), a protein that plays a role in numerous cellular processes that involve the control of intracellular hydrogen ions (Akhter, Nath et al. 1999). As a consequence of this activity, it was proposed that squalamine might find utility in treating diseases, including viral infections, where NHE3 played a critical role, and where its inhibition (by squalamine) could be effected (see e.g., U.S. Pat. No. 6,962,909). It has been proposed that squalamine could be used to treat viral infections should it be known that a specific virus infected a target cell expressing an NHE sensitive to inhibition (NHE-3 in the case of squalamine), and that the specific NHE played a critical role in the cellular homeostasis of that cell type, and that the virus in question naturally infected that cell type in the course of a disease process (U.S. Pat. No. 6,962,909). To date, however, no example of an NHE-3 dependent viral infection has been reported in the literature, nor has any known NHE-3 inhibitor been shown to exhibit antiviral activity in an animal, including squalamine. Furthermore the viruses demonstrated to be inactivated in vitro by squalamine, namely HIV and HSV (WO96/08270) are now known to infect cells via a pathway that is “pH independent”, in the sense that inhibitors of pH homeostasis do not influence infectivity (Pelkmans and Helenius 2003).
1436 is an aminosterol, isolated from the dogfish shark, structurally related to squalamine (U.S. Pat. No. 5,840,936; Rao, Shinnar et al. 2000). Aminosterol 1436 exhibits antiviral activity against HIV in tissue culture (U.S. Pat. No. 5,763,430) via a mechanism proposed to involve inhibition of a lymphocyte-specific NHE by 1436, resulting in suppression of cytokine responsiveness, and subsequent depression of the capacity of the lymphocyte to support HIV replication (U.S. Pat. No. 5,763,430). Aminosterol 1436, however, has an additional pharmacological property, not shared with squalamine, namely potent appetite suppression and promotion of dose-dependent weigh loss (U.S. Pat. No. 6,143,738; Zasloff, Williams et al. 2001; Ahima, Patel et al. 2002). Administration of Aminosterol 1436 to animals at doses that would achieve tissue concentrations of Aminosterol 1436 speculated to exert an antiviral benefit cause profound weight loss and suppression of food intake and death due to starvation (Zasloff, Williams et al. 2001; Ahima, Patel et al. 2002).
Recent patents have been issued describing squalamine like compounds with potent antibacterial activity, but no mention is made of their utility as antiviral agents (U.S. Pat. Nos. 5,834,453; 6,017,906). Indeed, the potential value of squalamine and its analogs as systemic agents has been questioned due to the extensive binding to albumin exhibited by these compounds (U.S. Pat. No. 5,834,453).
Squalamine in its intravenous form, squalamine lactate, is in the process of being tested as a treatment of fibrodysplasia ossificans progressiva, a rare disease where connective tissue will ossify when damaged. (Genesis, A., “Squalamine trial for the treatment of fibrodysplasia ossificans progressiva initiated”, Angiogenesis Weekly, 8:45 (2002).) Squalamine is also undergoing trials for treatment of non-small cell lung cancer (stage I/IIA) as well as general phase I pharmacokinetic studies. (Herbst et al., “A Phase I/IIA Trial of Continuous Five-Day Infusion of Squalamine Lactate (MSI-1256F) Plus Carboplatin and Paclitaxel in Patients with Advanced Non-Small Cell Lung Cancer 1”, Clinical Cancer Research, 9:4108-4115 (2003); Hao et al., “A Phase I and Pharmacokinetic Study of Squalamine, an Aminosterol Angiogenesis Inhibitor”, Clin Cancer Res., 9(7): 2465-2471 (2003).) In 2005, the Food and Drug Administration granted squalamine Fast Track status for approval for treatment of age-related macular degeneration. (CATE: California Assistive Technology Exchange”, California Assistive Technology Exchange, http://cate.ca.gov/index.cfm?a=Resources&p=News&article=176, Retrieved 2009-03-31.) However, Genaera Corporation discontinued trials for the use of squalamine in treating prostate cancer and wet age-related macular degeneration in 2007. (“PROSTATE CANCER; Genaera Discontinues LOMUCIN in Cystic Fibrosis and Squalamine in Prostate Cancer Studies”, Drug Week, pp. 251. 2007-07-20; “Reports describe the most recent news from Genaera Corporation”. Biotech Business Week, pp. 1540 (2007-09-17).) Squalamine is also marketed under the brand name Squalamax™ as a dietary supplement, though it has not been approved as a drug in this form and thus cannot make therapeutic claims. Squalamax™ is an unfractionated extract of shark liver, containing innumerable uncharacterized substances in addition to squalamine, itself present below 0.01% of the total weight of the extract. (“Cyber Warning Letter”, Center for Drug Evaluation and Research (2002-05-06), http://www.fda.gov/CDER/warn/cyber/2002/CFSANnuGen.htm; Retrieved 2009-03-31.) Moreover, the dietary supplement form of squalamine is not pharmaceutical grade squalamine, which requires significantly greater manufacturing efforts.
By 2006, over 300 patients had received squalamine in doses ranging from 6-700 mg/m2/day by iv administration, in three Phase I and nine Phase II studies (Hao et al., “A Phase I and pharmacokinetic study of squalamine, an aminosterol angiogenesis inhibitor,” Clin Cancer Res 9, 2465-71 (2003); Herbst et al., “A phase I/IIA trial of continuous five-day infusion of squalamine lactate (MSI-1256F) plus carboplatin and paclitaxel in patients with advanced non-small cell lung cancer,” Clin Cancer Res 9, 4108-15 (2003); Bhargava et al., “A phase I and pharmacokinetic study of squalamine, a novel antiangiogenic agent, in patients with advanced cancers,” Clin Cancer Res 7, 3912-9 (2001); and Connolly et al., “Squalamine lactate for exudative age-related macular degeneration,” Ophthalmol Clin North Am 19, 381-91, vi (2006). The studies showed that the compound exhibited an acceptable safety profile and evidence of efficacy in these early trials. In 2006 development of squalamine was halted for economic/strategic reasons by Genaera, and has remained in a dormant stage since.
There is a need in the art for new treatments for viral infections. There are a wide variety of viral diseases having limited or ineffective treatments. The present invention addresses the problem by providing a new method of treating and/or preventing viral infections.